The present invention relates to a color copier, color printer, color facsimile apparatus or similar color image forming apparatus.
The problem with a color image forming apparatus is that any deviation of, e.g., the distance between adjacent image forming sections or the position or angle of the individual image forming section from ideal one causes colors to be brought out of register on an output image. Let this kind of deviations be referred to as regular deviations. Such misregister lowers the quality of the output image. To solve this problem, it has been customary with this kind of apparatus to determine, before actual image formation, the amount of deviation of a register position color by color, and correct the deviation.
However, the conventional correction is effective only with the regular deviations ascribable to, e.g., the degree of mounting accuracy of the individual unit and the varying ambient temperature. In practice, there also occur variation in dot position and pitch and having a particular period due to variation in the speed of the individual photoconductive drum and the speed of a conveyor belt. Let this kind of deviations be referred to as irregular deviations. As a result, the image quality available with the conventional apparatus not dealing with the irregular deviations is limited.